JPS593907A - Molded transformer - Google Patents

Abstract

PURPOSE:To prevent separation of a conductive film effectively and obtain a transformer with surface shield of high safety, by a method wherein a conductive film is divided into at least four sections, at least two in the coil circumferential direction and at least two in the coil axial direction. CONSTITUTION:On surface of a resin layer 4 of a mold coil except portion around a line terminal 5 and a tap terminal 6, a shield layer (hatched portion) 7' is installed and divided into at least four sections, at least two in the coil circumferential direction and at least two in the coil axial direction, by narrow gaps 8 and separating bands 10. In order to prevent the shield layer 7' from forming one turn around a core, the narrowed gaps 8 are so arranged that the shield layer 7' is separated completely at one position or more. Sections of the shield layer 7' divided by other separating bands 10 are partially connected to other sections at one position or more by a conductive film 11 of narrow band form. In this constitution, all sections of the shield layer 7' can be connected electrically and grounded commonly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molded transformer with a surface shield that is safe even if a human body touches the surface of the molded coil during energization.

FIG. 1 is a diagram showing an example of the configuration of a conventional general molded transformer, where 1 is an iron core and 2 is a molded coil combined with the core. Figure 2 is a perspective view of the molded coil, Figure 6
The figure is a sectional view taken along line A-A', and as shown in this figure, the molded coil 2 is constructed by covering a bare coil 6 with an insulating resin layer 4, and is completely insulated except for the line terminal 5 and tap terminal 6. has been done. However, in such a normal molded transformer, in addition to the capacitance C1 between the coil conductor and the ground due to the insulating resin layer 4, as shown in the equivalent circuit in Figure 4, there is also a static capacitance C1 between the resin layer surface and the top and bottom. A capacitance C2 exists. Therefore, when the molded transformer is energized, the surface of the resin layer has a considerably high potential, and there is a risk of electric shock if a human body touches the surface of the resin layer.

FIG. 5 shows a molded coil with a surface shield (Japanese Patent Application No. 56-179670) devised to eliminate this danger. This molded coil 2' with a surface shield has a line terminal 5 on the surface of an insulating resin layer 4 that covers the bare coil.
, aluminum or zinc is thermally sprayed except for the periphery of the tap terminal 6 to form a shield layer 7 (shown with an extra line) made of a conductive film having a thickness of 20 to 200 μm. 8 is a narrow gap (a part where the shield layer is loose) provided at one place on the circumference in order to prevent the shield layer 7 from forming one turn around the iron core, and this shield layer 7 is connected to the ground wire 9. By connecting to the molded coil, most of the surface of the molded coil is kept at zero potential even during energization to prevent electric shock.

However, the linear expansion coefficient of the conductive film forming the shield layer is generally different from that of the molded coil, and the linear expansion coefficient of the molded coil type resin (for example, Hitachi's new MT resin has a linear expansion coefficient of 2.6).
Aluminum (linear expansion coefficient 2.3 x 10 /℃) or zinc (linear expansion coefficient 3.3
Even when using a thermal spray coating such as x10/℃), the shield layer and the resin layer exhibit different expansion and contraction amounts due to temperature changes when the coil is energized and stopped, and the difference in expansion and contraction amount exceeds the limit. Then, peeling occurs at the boundary between the shield layer and the resin layer. In the process of cooling and hardening the film immediately after thermal spraying, the surface of the film in contact with the air drops in temperature faster, and the surface in contact with the resin layer drops in temperature slower. A stress is generated that tends to cause the resin layer to peel off. Due to these causes, in the conventional technology, the larger the surface area of the shield layer and the larger the molded coil, the more easily the shield layer peels off, making it difficult to form a stable surface shield layer.

An object of the present invention is to eliminate the above-mentioned difficulties and provide a molded transformer with a surface shield that can maintain a stable electric shock prevention function for a long period of time and has higher safety.

It is believed that the stress caused by the difference in the amount of expansion and contraction between the shield layer and the resin layer due to the temperature change mentioned above and the difference in the shrinkage rate on both sides when the thermal spray coating is cooled and hardened are both proportional to the planar dimension of each shield layer. It's fine. The present invention focuses on this point, and by dividing the conductive film forming the surface shield layer of the molded coil into two or more sections in the coil circumferential direction and two or more sections in the coil axial direction, a total of four or more sections, The effective planar dimension of each shield layer is reduced to reduce the absolute value of the amount of expansion and contraction.

An embodiment of the present invention will be described below with reference to FIG.

Various methods can be considered for forming the conductive film of the shield on the surface of the resin layer of the molded coil, such as coating with conductive paint, plating, thermal spraying, etc., but as an example, zinc thermal spraying will be described.

In Fig. 6, masking tape is pasted in advance around the terminals on the surface of the resin layer 4, the narrow gap 8, and the separation zone 100 where a shielding layer is not desired, and a zinc spraying device is used to coat the resin layer 4 with a thickness of 20 to 200 μm. After forming the conductor film,
By peeling off the masking tape, line terminal 5,
Resin layer 4 of the mold-coil excluding the area around the tap terminal 6
A shield layer (shown with diagonal lines) 7' is provided on the surface of the shield layer 7', which is divided into four or more sections, two or more in the coil circumferential direction and two or more in the coil axial direction, by the narrow gap 8 and the separation band 10.

In order to prevent the shield layer 7' from forming one turn around the core, the narrow gap 8 is provided so as to completely divide the shield layer 7' at at least one point on the circumference. Each section of the shield layer 7' divided by the other separation strips 10 is partially connected to other sections at one or more points by a thin strip-shaped conductive film 11. By doing this, all sections of the shield layer 7' are electrically connected,
Can be commonly grounded.

It is sufficient to provide the shield layer 7' in an area that may come into contact with the human body during use, and the shield may be omitted near the center of the inner periphery of the molded coil where it is difficult for people to reach.

The size of one section of the shield layer 7' is determined according to the coefficient of thermal expansion of the insulating resin layer 4 and the shield layer 7', the thickness of each layer, etc., and the width of the narrow gap 8 and the separation zone 10 is determined so as not to impair safety. A molded coil 2 with a surface shield having a narrow width of about 1.5 mm is used as a broom 1. As shown in the figure, a molded transformer is constructed in combination with the iron core 1, and all sections of the shield layer 7' are grounded by the ground wire 9.

In the molded transformer with a surface shield according to the present invention, the shield layer 7 on the surface of the molded coil is formed of a conductive film that is subdivided in the coil circumferential direction and axial direction.
The absolute value of the stress caused by the difference in the amount of expansion and contraction between the shield layer and the resin layer when the temperature changes due to energization and rest of the coil decreases as the planar dimension per section of the shield layer decreases. In the case of forming a thermal spray coating, the absolute value of the stress generated due to the difference in shrinkage speed between both surfaces during cooling and hardening of the thermal spray coating also decreases. For this reason.

If the size of one section of the upper layer of the seal is determined appropriately, there is almost no need to worry about the shield layer peeling off.

Even if the shield layer is damaged by external force, it can be partially repaired relatively easily.

In this embodiment, each section of the shield layer 7' is only partially connected to other sections by the thin strip-shaped conductive film 11, so that it is effectively almost equivalent to an independent section. However, the peeling prevention effect □ can be further enhanced by shifting the positions of the strip-shaped conductor films 11 that connect the respective sections so that they are not lined up in a straight line.

As described above, according to the present invention, the molded coil has a highly safe surface shield that can effectively prevent peeling of the conductive film that forms the surface shield layer and maintain a stable electric shock prevention function for a long period of time. Molded transformers can be provided.

[Brief explanation of drawings]

Figures 1 (a) and (b) are front and side views showing an example of a conventional molded transformer, Figure 2 is a perspective view of its molded coil, and Figure 6 is its A, -A' sectional view. FIG. 4 is an equivalent circuit diagram thereof, FIG. 5 is a perspective view of a molded coil with a surface shield according to the prior art, and FIG. 6 is a perspective view of a molded coil with a surface shield according to an embodiment of the present invention. 1... Iron core 2... Molded coil 2' without surface shield...
Molded coil 4 with surface shield...Insulating resin layer
5... Line terminal 6... Tap terminal 7... Undivided shield layer 7'... Divided shield layer 8... Narrow gap 9... Earth wire 1.0
... Separation band 11 ... Band-shaped conductive film that connects each section of the shield layer Patent attorney Junnosuke Nakamura 1'1 Figure (Q) (b) Figure 2 Figure 3 Volume 4 Figure 4

Claims (2)

[Claims] (1) In a molded transformer constructed by combining a molded coil covered with an insulating resin layer with an iron core, the resin layer surface of the molded coil, excluding the area around the terminals, has a total of 2 or more in the circumferential direction of the coil and 2 or more in the axial direction of the coil. 1. A molded transformer comprising a shield layer made of a conductive film divided into four or more sections, and all sections of the shield layer are grounded. (2) The molded transformer according to claim (1), wherein all sections of the shield layer are partially connected to other sections by a band-shaped conductive film.